OnychoteuthisLichtenstein, 1818

This genus has contained four generally recognized species until recently; present accounts place the number at ~10, and more undescribed species probably exist.

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Introduction

Members of the genus are mostly small to medium sized squids of under 20 cm in mantle length as adults. The largest, however (O. borealijaponica) reaches a size of 350 mm ML (Kubodera et al. 1998). Species are found mostly in tropical and subtropical waters throughout the world's oceans although they are also common in high latitudes of the North Pacific, where O. borealijaponica reaches subarctic waters. One of the diagnostic features of Onychoteuthis species is the presence of one bilobed photophore (or two smaller, separate photophores, in O. horstkottei) on the ventral surface of each eyeball as seen in the photograph below (right). Another diagnostic feature is the presence of two photophores (arrows) on the viscera, as can barely be seen through the mantle in the photograph below (left).

Species of Onychoteuthis are commonly seen in surface waters at night and are often collected by dipnet at nightlight stations. Only young squid are normally captured in standard midwater trawls; apparently older squids avoid the trawls. One non-standard method of collection results from individuals being able to leap high out of the water and, sometimes, land on the deck of a ship. The type specimens of O. bergii were collected in this way: 'Our two specimens came to us as part of the rich inheritance of specimens from our brave Bergius, who died in the Cape of Good Hope in January of this year of tuberculosis, the victim of his own tireless efforts at collecting and observing plants and animals. His journal from the voyage reveals that these specimens flew on board the ship one night. One was found the following morning on the foredeck, the other in the crow’s nest, thirty feet above the sea surface, more evidence to support Aristotle’s remarks on their power of flight. The very elastic lateral flaps or fins may be of particular use in this respect. This occurred in May, 1816, approximately 100 miles west of the Cape. I have heard from other seafarers that other similar animals were collected in this way at about the same time.' (Translated from Lichtenstein 1818.)

Brief diagnosis:

Characteristics

Arms

Arm suckers with distal, fleshy thickening (see arrows in photograph below) in most species. This delicate thickening or knob is not obvious on all suckers and when present it is easily damaged during capture.

Protective membranes low and with trabeculae fused to sucker base and not clearly seen as separate entities (see photograph below).

8-13 occipital folds present on each side of head. Arrows in the photograph below indicate the ventral 7 occipital folds. Additional very small dorsal folds are out of focus and not visible in the picture. The olfactory organ is at the posterodorsal end of occipital fold II.

Behavior

Paralarvae of Onychoteuthis, like the paralarvae of many other squid, have the ability to withdraw their head and arms into their mantle cavity. This behavior is, presumably, defensive.

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Figure. Ventral views of a paralarva of O. compacta, head extended and retracted, off Hawaii. Photographs.

Life History

Most paralarval Onychoteuthis are easily recognized by the pointed rostrum on the gladius. If the fins are damaged, the rostrum projects well beyond the fins (see photographs of the paralarvae in the previous section). The photograph on the left (ventral view, posterior end of a paralarva) shows the rostrum barely emerging and the photograph on the right (side view, posterior end of a paralarva) shows the rostrum just reaching to the edge of the fins. Even if the rostrum is not protruding due to damage, it still can be easily seen.

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Figure. Ventral and side views of posterior ends of Onychoteuthis sp. paralarva, off Hawaii. Photographs by R. Young.

The adult female looses its tentacles apparently near the time of spawning. Spent females which are very flaccid were originally described as belonging to the genus Chaunoteuthis. In the photograph below the upper white arrow points to a scar that parallels much of the sissors cut through the mantle. This scar was apparently made by the male when mating. The lower arrow points to one of about 9 spermatangia embedded in the mantle muscle that apparently entered at the scar.

Page: Tree of Life
OnychoteuthisLichtenstein, 1818.
Authored by
K.S.R. Bolstad, Michael Vecchione, Richard E. Young, and Kotaro Tsuchiya.
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